1. Field of the Invention
This invention relates generally to gas generating compositions and, in particular, to such compositions which are suitable for inflating cushions (commonly known as "crash bags" or "air bags") in vehicle restraint systems of the types which utilize such a cushion to protect vehicle occupants upon sudden stopping or deceleration of the vehicle in which they are riding.
2. Description of the Prior Art
The use of protective gas inflated bags to cushion vehicle occupants in a crash situation is now widely known. In the first devised systems of this type, a quantity of compressed, stored gas was employed to inflate a crash bag which upon inflation was imposed between the occupant and the windshield, steering wheel and dashboard of the vehicle. However, because of the bulk of the apparatus, its generally slow reaction time and its maintenance difficulties, this stored pressurized gas system has now largely been superseded by systems which generate gases by the ignition of a chemical gas generating pyrotechnic composition.
A large number of quick-burning gas generating compositions have been developed for crash bags, although many tend to be deficient in one respect or another. Consequently, the industry has attempted to develop a gas generating composition which combines the essential features of a short induction period, a burn rate which is rapid but without any explosive effect, a high bulk density so that only a small amount of composition is required to produce large amounts of gas; the production of only non-toxic gases so that vehicle occupants are not endangered in the event of a leak or during the venting of the crash bag after inflation; the production of gases at a relatively low temperature so that damage to the crash bag is minimized and vehicle occupants are not burned; and good filterability of the reaction products so that hot solid residue cinders are easily removed from the gas stream. In addition, the gas generator composition must be readily formable into the required shape, and must be physically strong as well as chemically and physically stable so that long periods of storage can be attained under a under a wide range of temperature cycling and shock. While some of these desirable properties are found in known chemical gas generators, heretofore it has not been possible to provide compositions which satisfy all of the industry requirements.
One of the most common types of chemical gas generating compositions comprise a mixture or blend of an alkali metal or alkaline earth metal azide, usually sodium azide, and an oxidizer, commonly a metal oxide. In some cases the metal oxide is replaced by a metallic chloride, nitrate, sulfate, peroxide, perchloride, or other oxidizer.